(CNN) - Former Guatemalan President Alvaro Colom and a former finance minister who is now Oxfam International's chairman were detained Tuesday in a corruption investigation involving a public bus deal, the office of Guatemala's attorney general said.

Colom was detained on corruption charges along with nine other people, including Juan Alberto Fuentes Knight, chairman of Oxfam International.

The arrests come as Oxfam is under scrutiny in a sex scandal involving UK aid workers in Haiti. The corruption investigation relates to a public bus deal during Fuentes' service as Guatemala's finance minister, and has nothing to do with Oxfam.

Oxfam International Executive Director Winnie Byanyima said the aid organization does not know the nature of the formal charges against Fuentes.

"However, he has been entirely open with his Oxfam board and executive that he has been among former officials being investigated as part of a budgetary transaction made by the Guatemalan government while he was a finance minister," Byanyima said in a statement.

Fuentes assured Oxfam that he has cooperated fully with the investigation in the confidence he did not knowingly transgress rules or procedures, Byanyima said.

Fuentes told CNN's Michelle Mendoza on Tuesday that he was one of the signatories for the agreement with the company that operated the transportation service. But he said that when he noticed irregularities he asked for the contract to be investigated.